Radioactive transuranic liquified wastes produced by nuclear facilities present a difficult problem in terms of storage. Typically, these wastes are stored on site in large stainless steel tanks. Due to the limited capacity of existing storage tanks, industry has sought effective means for reducing the volume of transuranic wastes.
Prior art attempts to effect volume reduction by drying and melting radioactively contaminated slurries have used some what complicated mechanical structures such as "wiped-film evaporators" and "extruders". A wiped-film evaporator is described in a publication entitled "Wiped-Film Evaporators for Evaporating Alkaline Light Water Reactor Radioactive Wastes", by C. B. Goodlett in Nucl. Tech., 43, pp. 259-267, (April, 1979). An extruder is described in a publication entitled "Twin-Screw Compounding" by D. F. Mielcarek in Chem. Engr. Prog., pp. 59-67 (June, 1987). Both types of devices require moving parts and bearings that are prone to wear and corrode when exposed to hot, abrasive, and corrosive chemical slurries. Moreover, both processes require a mechanical process mover to wipe a thin slurry film on an externally heated casing to dry the slurry. Also, some means of conveying the hot slurry is required to prevent build-up in both the wiped-film evaporator and the extruder.
Microwave heating of radioactive wastes has been described in several publications. For example, U.S. Pat. No. 4,514,329 to Wakabayashi et al. describes the treatment of radioactive waste with microwave energy, but the process relates to high temperature vitrification into glass. U.S. Pat. No. 4,563,335 to Akiyama et al. describes a device for concentrating and denitrating a nitrate solution by using microwave energy. However, this reference also requires moving parts to transport the final product and is thus not Hardwick et al. describes a treatment process for high level nuclear wastes in which microwave energy is used to create a glass wasteform.
Other publications that describe other microwave applications to nuclear waste treatment include the following U.S. Pat. Nos.: 4,040,973 to Szivos et al., 4,778,626 to Ramm et al., 4,844,838 to Ohtsuka et al., 4,476,098 to Nakamori et al., and 4,565,670 to Miyazaki et al. In general, these references do not show in-drum processes and thus suffer from requiring moving parts and complex materials handling structures.